Fix the nullable parameter declarations for compatibility with PHP 8.4

[martio]

Q	A
Is bugfix?	✅/✖️
New feature?	✔️/❌
Breaks BC?	✔️/❌
Fixed issues	comma-separated list of tickets # fixed by the PR, if any

I have prepared a small fix that resolves the following issue:

DEPRECATED  Yiisoft\Translator\TranslatorInterface::translate(): Implicitly marking parameter $locale as nullable is deprecated, the explicit nullable type must be used instead in vendor/yiisoft/translator/src/TranslatorInterface.php on line 46.

Yiisoft\Translator\TranslatorInterface

   public function translate(
       string|Stringable $id,
       array $parameters = [],
       string $category = null,
       string $locale = null
   ): string;

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.35%. Comparing base (50dcaa5) to head (b3f3749).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #148   +/-   ##
=========================================
  Coverage     99.35%   99.35%           
  Complexity      111      111           
=========================================
  Files            13       13           
  Lines           308      308           
=========================================
  Hits            306      306           
  Misses            2        2           

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[vjik]

@martio Thank you 👍